Can't scan from printer control panel on Canon Pixma MG5270

I have just connected my Canon Pixma MG5270 to my iMac running OSX 10.7.3 via WiFi. Printing works great, and scanning from the desktop "Canon MP Navigator EX - MG 5200 series" V 4.0.3 application works like a dream. When I try to scan via the operations panel on the printer/scanner the following comes up - Set the PC to start scanning". This worked fine when connected directly via USB cable. I have searched the web and believe I have the correct settings, particuliarly in MP Navigator:

1. Main Menu -> One-click -> Start scanning by clicking the button (checked)

2. Main Menu -> One-click -> Preferences -> General -> Compress scanned images when transferring (checked) -> Change -> Network Device List (selected Canon MG 5200 series_xxxxxxxxx) -> Scan-from-Operation-Panel Settings -> Network Device List (selected Canon MG5200 series_xxxxxxx)

I have restarted the iMac and printer and always with the same result.

Any help appreciated!!